Massive waves slamming into California's coast - killing at least one person and causing millions of dollars in damage - are being labelled the "New Zealand surf" because of where they are coming from.

In a rare event, a big weather system between New Zealand and Antarctica has generated a heavy Pacific wide swell, bringing the waves to California.

Sean Collins, chief forecaster and president of Surfline, told news website Patch.com he warned Californian authorities over the swell.

"Extra caution is urged to keep the public aware and safe from these large waves and associated rip currents."

He said it was one of the biggest swells to hit with some waves coming ashore at six to seven metres.

Collins said southern hemisphere storms routinely produced waves in California, but this latest one was in the top 10 percent of known waves.

The US National Weather Service has warned beachgoers were urged to swim only near lifeguard towers - or to stay on the sand.

"Have a good time watching the waves but stay out of the water if you're not experienced," National Weather Service forecaster Eric Boldt said.

The rough surf was caused by the swell from a powerful storm in New Zealand, where it is winter.

"It had 50-foot waves down there when it was going at its peak. The energy came up here," Boldt told the Associated Press.

The heavy surf chewed up the sandy bottom, creating potholes that can dunk unwary swimmers and contributing to dangerous rip currents.

"That probably kills more people in Southern California than any other phenomenon." said Boldt.

One news website said many people went to the coast to look at the relentless armada of waves building up and then smashing down along the shore.

"A winter storm off New Zealand is credited with generating the awe-inspiring swell along the Southern California coast," it reported.